Tobacco smoking by adolescents poses a major health threat, with 90% of adults having initiated smoking before the age of 18. The long-term objective of this research is to investigate ways to effect decreases is smoking among adolescents. The major purpose of this study is to examine whether brief, individual motivational interviewing (MI) treatment in a hospital emergency department (ED) followed by a booster session one week later can be effective in changing subsequent smoking behavior in a population of adolescent ED patients. The effectiveness of the intervention will be determined by randomly assigning adolescent smokers to either standard care of MI plus booster, and then comparing groups at 1, 3, 6, and 12- month follow ups on self-report and biochemical measures. Motivational Interviewing has been selected as the experimental intervention because of its demonstrated promise as a brief intervention in medical settings, and its appropriateness for a population of smokers which will include a full range of motivation to change. MI's effect on behaviors and cognitions related to quitting smoking will also be assessed, including: effects on number of quit attempts, total duration of abstinence, treatment seeking for smoking cessation, motivation to change smoking behavior, negative evaluation of smoking consequences. In order to identify individuals most likely to benefit from MI, the mediating effects of several baseline characteristics will be explored, including level or nicotine dependence, stage of motivation to change smoking behavior, depressed affect, and use of other drugs. Instrument development is also a focus of the work to be accomplished. The importance is this work is its potential for providing a cost-effective brief intervention to reduce smoking among adolescents. Because it is implemented in the ED, it reaches a high-risk population of adolescents that would be difficult to reach elsewhere, i.e., youth who have dropped out of school and youth who do not receive health care outside the ED setting.